This invention relates to a process for the continuous coagulating and consolidating the coagulated latex as a fluid paste coagulum, said paste being a uniform mixture of a high viscosity fluid phase and a low viscosity fluid phase, said phase being immiscible in one another.
U.S. Pat. No. 3,859,217 discloses an apparatus for continuously separating immiscible high viscosity fluids from low viscosity fluids by shearing screws wherein drag forces carry the more viscous fluid forward leaving the less viscous phase behind as a separated phase. Such devices will operate more efficiently if the two phase are uniformly mixed on a continuous basis and can be fed as a uniform paste to such separating devices.
Hence, there is a real need for continuous mixing process that can coagulate latices and form such coagulated latices into forms such as fluid pastes that can be readily handled in downstream processing. Generally, the solid polymer of polymer latices must be recovered from such latices. Prior art processes have used batch operations wherein the latex is coagulated with electrolyte and the polymer filtered from the water phase. Such processes are higher cost, are not readily controlled on a continuous process basis and suffer from loss of fine precipitated polymer during filtration or centrifugation.
The present process provides for continuous coagulation and inversion of phases so that the polymeric phases become the continuous phase of the paste and the immiscible water phase can be readily separated from the paste.
There has now been discovered a new and very useful process for continuously mixing an aqueous latex with an aqueous coagulating medium uniformly so that polymer phase of an aqueous latex is coagulated and partitioned from the aqueous phase into a solvent phase as a oil phase having the water phase dispersed therein providing a consolidated coagulum paste that can be uniformly fed to a separator for separation of the low viscosity aqueous phase.
In particular, rubber latices that have the rubber particles grafted with monomers by emulsion polymerization may be recovered from the latex, dispersed in additional monomer and mass polymerized to form rubber reinforced polyblends.
The grafted rubber latices, hence, may have the monomers added first, without coagulating the rubber particles, and then fed to the mixing apparatus of the present invention along with a coagulating medium such as an aqueous metal salt solution. As the salt mixes with the aqueous emulsion of the rubber particles, it breaks the water emulsion and the rubber particles are partitioned into a monomer or solvent phase as a oil phase having the water-salt phase dispersed therein with the coagulum taking the form of a fluid paste.
The process for continuously mixing the latex and coagulant must effectively mix the two and consolidate the dispersed oil phase formed into a continuous fluid paste having the water phase dispersed therein. This is accomplished by a novel combination of wiper-densifier blades which by mechanical pressure at the barrel wall densifies the tacky rubber-solvent oil phase into a continuous phase separating the water into a dispersed water phase. The forward, angled, tab blades pick up the densified paste at the wall and forward it along the barrel for additional working and consolidation by the wiper densifier blades.
The apparatus then has a novel arrangement of angled tab blades for forwarding and mixing in combination with wiper densifying blades to produce, during the operation of said apparatus, a discharged consolidated coagulated paste.